Method of making rotors for variable capacitors

ABSTRACT

A method of making rotors for variable capacitors which employs a thin glass plate and a thicker backing glass plate onto each of which is positioned an array of metalized electrodes in identical patterns. The plates are juxtaposed to place the electrodes in registration and the assembly of plates is then fired to fuse them and form an integral monolithic glass body with electrodes of the thin plate embedded in the glass body. Holes are bored in the glass body through the electrodes and the electrodes are then electrically connected together by metalizing interiors of the holes. The rotor discs are then cut out of the glass body, each disc including one pair of registering electrodes. Conductive members are then added to complete the rotor assembly.

United States Patent 1 1 3,681,828 Mezey 51 Aug. 8, 1972 METHOD OFMAKING ROTORS FOR VARIABLE CAPACITORS [72] lnventor: hank G. J. Meuy,115 Monroe Drive, Centerport, NY. 1 1721 [22] Filed: May 21,1970

[21] Appl.No.: 39,440

[52] US. Cl. .....................29/25.42, 264/58, 264/61, 264/67,317/253, 317/261 [51] Int. Cl. ..H0lg 13/00 [58] Field of Search..29/25.42, 25.41; 317/253, 254, 317/261; 264/58, 61, 67; 156/306, 89

[56] References Cited UNITED STATES PATENTS 2,839,816 6/1958McGraw...................29/25.42 3,189,974 6/1965 Fabricius ..29/2S.423,244,951 4/1966 Wallace ..3l7/249 3,235,939 2/1966 Rodriquez et a1...29/25.42 3,506,895 4/1970 Kellerman ..3l7/261 Primary Examiner-John F.Campbell Assistant Exandner-Carl E. Hall Attorney-Edward H. Loveman [57]ABSTRACT A method of making rotors for variable capacitors which employsa thin glass plate and a thicker backing glass plate onto each of whichis positioned an array of metalized electrodes in identical patterns.The plates are juxtaposed to place the electrodes in registration andthe assembly of plates is then tired to fuse them and form an integralmonolithic glass body with electrodes of the thin plate embedded in theglass body. Holes are bored in the glass body through the electrodes andthe electrodes are then electrically connected together by metalizinginteriors of the holes. The rotor discs are then cut out of the glassbody, each disc including one pair of registering electrodes. Conductivemembers are then added to complete the rotor assembly.

7 Claims, 10 Drawing Figures PATENTEUAUB 8 n 6 3.881.828

sumwz' 58 FIG. 9

APPLY SEMI-CIRCULAR METAL ELECTRODES TO GLASS PLATES; LARGER ELECTRODESON ONE SIDE OF THICKER GLASS PLATE. SMALLER ELECTRODES ON ONE SIDE OFTHINNER GLASS PLATE.

BOND GLASS PLATES TOGETHER TO FORM MONOLITHIC 11/ BODY WITH LARGERELECTRODES ON ONE OUTER SIDE AND WITH SMALLER ELECTRODES INSIDE THEMONOLITHIC BODY ADJACENT OTHER SIDE.

BORE HOLES IN MONOLITHIC STRUCTURE; METALLIZE III OFF CENTER HOLE TOCONNECT OUTSIDE AND INSIDE ELECTRODES.

LIT {CUT OUT CIRCULAR ROTOR DISCS.

Y IEOMPLETE ASSEMBLYOF ROTOR AND CAPACITOR.

FIG. IO

INVENTOR FRANK G. J. MEZEY ATTORNEY METHOD OF MAKING ROTARS FOR VARIABLECAPACITORS This invention concerns a method for making rotors forvariable capacitors and more specifically for a method of making solidstate monolithic rotors for variable capacitors.

Trimmer capacitors are well known in the art and are generally comprisedof a rotor having a metalized conductor portion which serves as oneplate of the capacitor. A stationary plate, also having a conductiveportion is mounted on a stator which rotably supports the rotor.Rotation of the rotor changes the capacitance between the conductiverotary plate and the stationary conductive plate. A typical capacitor ofthis type is described in US. Pat. No. 3,244,95 l.

I-Ieretofore considerable difficulties have been encountered inmanufacturing such variable capacitors in miniature sizes required bypresent day electronic circuits. The apparatus described in the abovementioned patent comprises a stack of thin, unfired flexible ceramicdiscs assembled prior to firing. One disc hasa metalized top portion.The assembly of discs is compressed under high pressure, i.e., tons ormore per square inch. Then the assembly is fired at high temperature tofuse the stack of discs into a monolithic structure. While such a methodcan theoretically lead to a useful rotor structure for a variablecapacitor it is not adapted to high precision mass productionmanufacturing requirements, because the rotors must be individuallyassembled by hand. The equipment, facilities and quality controlsrequired to handle flexible ceramic discs having a thickness of 0.02 in.or less and a diameter of 0.2 inch or less are very costly, and thepainstaking skill and labor time required preclude high productionrates.

The present invention is directed at a method of making a rotor for atrimmer capacitor which over comes the above and other difiiculties anddisadvantages of prior manufacturing methods. According to the inventiona multiplicity of thin semicircular spots of silver or other metallicpaste are applied in spaced array to one side of a thin sheet or plateof glass. This is done by silk screening, vapor deposition or someprinting process. Another multiplicity of semicircular metallic spots isapplied in a similar array to a thick plate of glass. If necessary theplates are heated sufficiently to drive off all volatile components ofthe metallic paste and to solidify and set the spots and thus formelectrodes as very thin films on the glass plates. The plates are thenplaced one on top of the other with the electrodes in registration witheach other but separated by the thickness of the thick glass plate. Theassembly is placed between ground and polish optically flat inert,infusable, plates or blocks. This assembly is then fired, preferably ina vacuum furnace. The glass plates fuse to each other to form amonolithic body with the metallic electrodes of the thinner plateembedded inside of the rigid solid glass body. Holes are drilled in theglass body through each vertical pair of electrodes which are thenelectrically connected together. Cylindrical discs emcompassing thevertical pair of electrodes are cut out of the monolithic body by coredrilling, ultrasonic machining or other suitable method to formindividual capacitor rotors. The rotors are then ready for assembly withother parts to form the complete variable capacitors. An importantfeature of the process is that a multiplicity of rotors can be madesimultaneously. The precise registration required between metallicelectrodes in all the rotors is accomplished by simply overlaying oneglass plate on the other. It is only when the rotor assemblies aresubstantially complete that they are cut of the monolithic glass body.This represents a radical departure from prior manufacturing methodswhere each rotor is individually assembled by hand.

Accordingly it is a primary object of the present invention to providefor improved method for manufacturing variable capacitor rotors.

Another object of the present invention is to provide a high-.precision, mass production manufacturing method for making trimmercapacitor rotors.

A more specific object of the present invention is to provide a methodof manufacturing a solid state rotor assembly comprised of a pluralityof extremely thin discs which do not have to be assembled individually.

These and other objects and many of the attendant advantages of thisinvention will be readily appreciated as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is an exploded perspective view of parts of an assembly of platesillustrating one stage of the manufacturing method according to theinvention;

FIG. 2 is an end elevational view of the plates of FIG. I in assembledposition at another stage in the manufacturing method;

FIG. 3 is an enlarged fragmentary sectional vie taken along line 3-3 ofFIG. 2;

FIG. 4 is a fragmentary enlarged top plan view of the monolithicstructure or body at another stage of the manufacturing method;

FIG. 5 is a fragmentary cross sectional view taken along line 5-5 ofFIG. 4;

FIG. 6 is a fragmentary top plan view similar to FIG. 4 showing themonolithic body at a further stage of the manufacturing method;

FIG. 7 is an enlarged top plan view of a single rotor disc as cut fromthe monolithic body of FIG. 6;

FIG. 8 is an enlarged cross sectional view taken along line 8-8 of FIG.7;

FIG. 9 is a cross sectional view showing part of a complete variablecapacitor assembly including the rotor disc of FIG. 7; and

FIG. 10 is a flow chart of steps in the manufacturing method accordingto the invention.

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts throughout the several views thereis shown in FIG. I to FIG. 3 a rectangular glass plate generallydesignated as reference numeral 10.

This plate may have a thickness ranging from 1 to 10 mils (0.001 to0.010 inch). On the upper surface of the plate is an array of extremelythin electrodes, generally designated as reference numeral 12, made of ametal suitable for capacitor plates. This metal may be silver, gold,palladium or the like. The pattern or array may be made by applyingspots of metal paste by silk screen, printing, vapor deposition or otherprocess capable of producing precisely defined and located thin films ona flat glass surface. The array of electrodes are preferablysemicircular and each electrode has a semicircular edge 14 and astraight diametral edge 16; however, these films could have elliptical,spiral, or other geometrical shapes. The metallization of plate 10 toform electrodes I2 is part of step I in the method outlined in the chartof FIG. 10. On another glass plate 20 which is materially thicker thanplate 10 is another array of metallized electrodes 22 each of which hasa semicircular edge 23 and a straight diametral edge 27. The array orpattern of electrodes 22 is identical to that of electrodes 12. Theapplication of electrodes 22 to plate 20 is also part of step I asindicated in the chart of FIG. 10. Plate 20 overlays plate 10 in theassembly 25 shown in FIGS. 2 and 3. Each electrode 22 registers withacorresponding electrode 12. The edges of the plates are readilydisposed in registration with each other by use of a simple jig orfixture (not shown).

Mere superposition of the plates 10 and 20 places all the electrodes 12and 22 in registration with each other. The electrodes 12 may beslightly smaller than the electrodes 22 to prevent arcing or voltagebreakdown between the electrodes 12 and the associated stator electrodein the completed variable capacitor. The electrodes I2 may beapproximately 0.2 inch in diameter, for example.

On opposite sides of the plates 10 and 20 are placed rectangulargraphite plates or blocks 30, 32 respectively. These blocks have ground,polished and optically flat inner surfaces 31, 33 juxtaposed to the topof the plate 20 and the bottom of the plate 10 respectively. The plate20 may have a thickness in the order of 0.0] to 0. I inch. In place ofgraphite, some other rigid, inert, infusible material such as a firedceramic may be used for the plates or blocks 30, 32. In the assembly 25which is held together by a suitable clamping fixture (not shown), itwill be noted that the electrodes 12 face the underside of the plate 20and the electrodes 22 are on the upper side of the plate 20. Theassembly 22 is placed in a suitable furnace such as a vacuum furnace andheated under vacuum or low pressure until the plates 12 and 20 fuse toeach other to form an integral, monolithic structure or body 40 shown inFIGS. 4 and 5. The electrodes 12 are embedded in the body 40 close tothe underside 42 of the body. The spacing may be as small as 0.00],which is much less than can be practicably obtained by prior methodssuch as the individual disc assembly method of the above mentioned US.Pat. No. 3,244,951. As a result, the variable capacitors finallyproduced may each have a maximum capacitance as much as twice as thatattainable in capacitors of the same size produced by prior methods. Thebonding together of plates and is indicated as step II in the chart ofFIG. 10. FIGS 4 and 5 show the alignment or registration of theelectrode 12 with each slightly larger electrode 22 in the body 40.

FIG. 6 shows the body 40 at a further manufacturing stage. I-lere holes44 and 46 have been drilled in the body 40. The holes 44 are larger andare located at the centers of the straight diametral edges 16, 23 of theelectrodes 12 and 22, respectively. It will be noted that the diametraledges 16 and 27 are in perfect registration while the arcuate edge 14 ofthe electrode 12 is slightly spaced from and within the arcuated edge 23of the electrode 22, as clearly illustrated in FIGS. 3 to 8. Each of theholes 44 is centrally drilled or bored entirely through the body 40 toserve as a center or axis of rotation of the rotor in the completecapacitor. On the other hand the holes46 are each drilled only throughthe body 40 down to the electrode I2 to expose a portion of thiselectrode at the bottom of the hole. The holes 46 are located off centeror eccentrically with respect to the centers of holes 44. The drillingof holes 44, 46 is indicated as part of step I" in the chart of FIG. 10.

After the holes 44, 46 are drilled, the interiors thereof are metallizedwith silver or other metal by vacuum deposition or other suitableprocess. This forms a cup shaped lining 48 for each hole 46 as clearlyshown in FIGS. 8 and 9, and serves as an electrical connector betweeneach pair of the electrodes 12 and 22. The metallizing of the off centerholes 46 is indicated as step III in FIG. 10. Circular discs 49 may nowbe cut out of the monolithic body 40 as indicated by dotted lines inFIG. 6. This is step IV in FIG. 10. The discs 49 are slightly largerdiametrally than the larger electrodes 22. FIGS. 7, 8 and 9 show thecircular discs 49 cut out of the body 40. The capacitor rotor may now beassembled to a stator to complete the assembly.

FIG. 9 shows a completed capacitor assembly 50. A rotor assembly 55includes the monolithic disc 49, the semicircular electrodes 12, 22, andthe connecting conductor 48. A screw 56 is inserted through a hole 44and is engaged by a sleeve nut 58. A head 57 of the screw 56 is securedby a solder joint 60 to the electrode 22. A head 62 of the nut 58 bearsagainst a metal spring washer 64 which bears on a flat metal washer 66.The washer 66 bears against a contact plate 68 applied to the undersideof an insulative plate 70. A wire 71 is secured by a solder joint 73 tothe plate 68. The sleeve nut 58 extends axially through a hole 72 inplate 70. A conductive stator plate 74 is secured to the upper side ofinsulative plate 70. A wire 75 is secured by a solder joint 76 to theplate 74. The rotor disc 49 bears the stator plate 74. The spacingbetween plate 74 and electrode 12 may be small as 0.001 inch. Thedielectric between the electrode 12 and the plate 74 is glass whichformerly formed part of the glass plate 10.

The variable capacitor is adjusted by turning the rotor 55. This may beaccomplished by engaging a tool such as a screwdriver in a slot 80 ofscrew head 57. The completion of the rotor assembly and the capacitorassembly is indicated as step V in the chart of FIG. 10.

It will be apparent from the foregoing detailed description of themanufacturing method that a plurality of capacitor rotors can besimultaneously produced. Individual handling of fragile glass or ceramicdiscs 0.00l inch or so in thickness is avoided. Perfect registration ofthe electrodes in all rotors is simultaneously effected. As many rotorscan be made at one time as desired, such as 10, 50, a or more All areprecision made. Manufacturing costs are thus minimized. Large savingsare effected in labor cost, time and materials. Much expensive, complexequipment required by prior manufacturing methods are not needed in thepresent method. The resulting products are additionally superior inprecision, higher in capacitance, and more rugged in construction.

Obviously, the foregoing disclosure relates to only preferredembodiments of the invention and that it is intended to cover allchanges and modifications of the examples of the invention herein chosenfor the purposes of the disclosure. which do not constitute departuresfrom the spirit and scope of the invention.

I claim: 1. A method of making rotors for variable capacitors,comprising the steps of:

discretely applying first electrodes in a first spaced array to a firstthin, fusible, fiat dielectric plate; discretely applying secondelectrodes in a second spaced array to a second fusible, flat,dielectric plate thicker than said electrodes on said first plate;stacking the side of said first plate having said first electrodesthereon to the side of said second plate, opposite the side said secondelectrodes are applied, such that each of said discrete first electrodesare vertically aligned with a corresponding discrete second electrode;firing said plates to bond them together and form an integral,monolithic body with said first electrodes embedded in said body; andcutting a plurality of discs out of said body with each disc containingone of said first electrodes and one of said second electrodes. 2. Amethod as defined in claim 1, further comprising the step of drillingfirst holes in said body to serve as centers of rotation for said discs,and second holes to expose portions of said first electrodes.

3. A method as defined in claim 2, further comprising the step ofinserting a conductive element in each of said second holes toelectrically connect each pair of aligned first and second electrodes.

4. A method as defined in Claim 1, wherein said discrete applying offirst electrodes and said discrete applying of second electrodes eachcomprises the step of metallizing films bonded respectively to saidfirst and second plate.

5. A method as defined in claim 2, further comprising the step ofmetallizing the interior of each of said second holes to connect eachpair of registering first and second electrodes mechanically andelectrically.

6. A method as defined in claim 1 wherein the step of firing said platecomprises the step of placing blocks on opposite sides of said first andsecond plates to form an assembly,

placing the assembly into a vacuum furnace and heating the furnace to atemperature such that said plates fuse to each other to form an integralmonolithic structure.

7. A method as defined in claim 6, further comprising the step ofclamping said rectangular blocks together to form a rigid assembly.

l i t

1. A method of making rotors for variable capacitors, comprising thesteps of: discretely applying first electrodes in a first spaced arrayto a first thin, fusible, flat dielectric plate; discretely applyingsecond electrodes in a second spaced array to a second fusible, flat,dielectric plate thicker than said electrodes on said first plate;stacking the side of said first plate having said first electrodesthereon to the side of said second plate, opposite the side said secondelectrodes are applied, such that each of said discrete first electrodesare vertically aligned with a corresponding discrete second electrode;firing said plates to bond them together and form an integral,monolithic body with said first electrodes embedded in said body; andcutting a plurality of discs out of said body with each disc containingone of said first electrodes and one of said second electrodes.
 2. Amethod as defined in claim 1, further comprising the step of drillingfirst holes in said body to serve as centers of rotation for said discs,and second holes to expose portions of said first electrodes.
 3. Amethod as defined in claim 2, further comprising the step of inserting aconductive element in each of said second holes to electrically connecteach pair of aligned first and second electrodes.
 4. A method as definedin Claim 1, wherein said discrete applying of first electrodes and saiddiscrete applying of second electrodes each comprises the step ofmetallizing films bonded respectively to said first and second plate. 5.A method as defined in claim 2, further comprising the step ofmetallizing the interior of each of said second holes to connect eachpair of registering first and second electrodes mechanically andelectrically.
 6. A method as defined in claim 1 wherein the step offiring said plate comprises the step of placing blocks on opposite sidesof said first and second plates to form an assembly, placing theassembly into a vacuum furnace and heating the furnace to a temperaturesuch that said plates fuse to each other to form an integral monolithicstructure.
 7. A method as defined in claim 6, further comprising thestep of clamping said rectangular blocks together to form a rigidassembly.